Electronic measurement of end point of asphalt oxidation

ABSTRACT

An electronic measuring technique for use in determining the end point of a process, such as an air blowing process employed in the manufacture of asphalt by means of an electronic bridge circuit, a device for monitoring continuously certain electrical properties of the actual product, and a reference standard which simulates the preselected desired electrical properties of the product, such as oxidized asphalt, being manufactured. As the process progresses the difference between the sensed electrical properties of the actual product and those simulated by the reference standard decreases and becomes zero or nearly zero at the end point. When the difference is zero, provision is made for the process to be stopped automatically or manually, whereupon the product is transferred into its respective storage area.

ilnited States Patent [1 1 Forster et al. [4 cc. 18, 1973 [54]ELECTRONIC MEASUREMENT OF END 3,462,364 8/1969 Carlson 23/230 A POINT OFASPHALT OXIDATIQN 3,540,868 ll/l970 Chevion 23/230 A [75] inventors ggag gzit zi i ggfg g ii t z Primary Examiner-Delbert E. Gantz AssistantExaminer-Veronica OKeefe Gathman, Belmar, all of NJ. Attorney nonald FWohlers [73] Assignee: Esso Research and Engineering Company, Linden,NJ. [57] ABSTRACT [22] Filed: July 12, 1972 An electronic measuringtechnique for use in determining the end point of a process, such as anair blow- [2]] Appl' 271036 ing process employed in the manufacture ofasphalt by R l t d Us, A li ti D t means of an electronic bridgecircuit, a device for [63] Continuation of Sen No 9,486 Feb 9, 1970'monitoring continuously certain electrical properties 9 of the actualproduct, and a reference standard which 52 us. Cl 208/6, 208/39, 208/44,simulates the preselected desired electrical Properties 23/23() A,324/258 of the product, such as oxidized asphalt, being manu- [51] Int.Cl C10g 1/00 facmred' AS the process progresses the difference [58]Field of Search 208/6, 44, 39; tween the sensed electrical Properties ofthe actual 23/23O A product and those simulated by the referencestandard decreases and becomes zero or nearly zero at the end [56]References Cited point. When the difference is zero, provision is madeUNITED STATES PATENTS for the process to be stopped automatically ormanually, whereupon the product is transferred to its re- 2,099,434 Il/l937 Culbertson, .lr. Spective Storage area 2,3l7,l50 4/1943 Lovell etal 208/6 3,090,223 5/1963 Juffa et al. 208/DIG. l 2 Claims, 3 DrawingFigures Pmmwnu: 1 8 I975 3; 779 I892 sum 1 or 2 Q I I I 24 qv REFERENCE26 EXCITATION STANDARD PRE AMP SECTION 1 TEST CELL PHASE I SENSITIVE IDETECTOR 5 3/ CAPACITANCE READOUT (33) PHASING PHASE SECTION SENSITIVE II DETECTOR I RESISTANCE READOUT (34) AITTESRNEY ELECTRONIC MEASUREMENTOil END PUHNT Oil ASPHALT UXTDATKON This is a continuation, ofapplication Ser. No. 9,486 filed Feb. 9, 1970.

BACKGROUND OF THE INVENTION The present invention relates to a systemwherein certain preselected characteristics of a product beingmanufactured are continuously monitored and compared with a referencestandard simulating desired characteristics of the product, whereby whenthe difference between the actual product characteristics and thereference standard is substantially zero, this is shown on a readoutdevice, thus making the operator aware that the desired end point hasbeen attained and the process may be stopped for transfer of the productto a storage area or the like. More particularly, the present inventionis concerned with a novel and improved electronic measuring system fordetermining the end point in a process employed in the manufacture of aproduct by means of an electronic device which comprises a sensor, suchas a test cell, mounted in the tank or tower containing the product andin contact therewith, a reference standard for simulating certainpreselected electrical properties of the product and an electronicbridge with a readout display for comparing the characteristics of theactual product and those of the reference standard thereby to provide anindication as to when the desired product characteristics, or in otherwords the process end point, have been obtained.

Although the present invention will be described with regard to apreferred embodiment involving asphalt oxidation, it will be apparent tothose skilled in the art that the invention generally is applicable toother plant operations. l-leretofore the duration of the air blowingprocess used to produce oxidized asphalt has been.

based on a semi-empirical relation between the length of time air isblown and the softening point. Generally, the operation requires thatair be blown through the asphalt at a temperature of 480 to 500F. forabout six hours to achieve an asphalt grade having a softening pointranging from 190 to 200F. (commonly known as ISO-or), or eight hours foran asphalt grade having a softening point range from 220 to 230F.(commonly known as '220-ox). At the end of the period required for therespective grades the air flow is stopped and a laboratory inspectionsample is removed. The asphalt then is kept at 480 to 500F. until thelaboratory reports its findings some two hours later. if the softeningpoint is found to be too low, air blowing is resumed for a relativelyshort period of time. if, on the other hand, it is too high, the asphaltis pumped into a storage tank for reblending. The foregoing procedurehas proven to be quite unsatisfactory because not only is productquality control very poor--in fact, inspection of the finished productshas revealed that only 40 to 50 percent of them are within the specifiedlimit-but the tower capacity is reduced by necessitating the holding ofthe product while awaiting inspection results. Further, the delay isobjectionable in terms of product quality, since it has been found thateven without air flow the viscosity and hence the softening point of theoxidized asphalt may increase during this waiting period. The termsoftening point as used in this specification is intended to mean thatthe temperature at which the asphalt contained within the confines of aring can no longer support the weight of a steel ball of a diametersmaller than the inner diameter of the ring. For a further detaileddescription of a method commonly employed in determining the softeningpoint, reference should be made to ASTM Method D36-66T.

Depending on the extent of the air blowing process, it is possible toproduce materials having desired softening points ranging from below 100to over 230F. The higher the softening point range the greater is theduration of air blowing required and thus, the time required for theproduct to remain in the tower is greatly increased and the totalthroughput, particularly during peak seasons, is reduced considerably.

Various attempts have been made to find a satisfactory way to increasethe capacity of the plant. To pro vide an additional tower is not veryattractive because the plant capacity is exceeded only during periods ofpeak demand. Another possibility is to blend one batch of the producthaving a softening point that is too high with another batch having acorrespondingly lower softening point. By blending the two in a storagetank, it is hoped that the final product will be within the establishedspecification and while this approach might yield an acceptablesoftening point, other physical characteristics have been found to beadversely affected. Also, since the residence time of theoffspecification batch in the storage tank might be very short, it isquite possible that it may be passed on to customers before blendingcould take place. Thus, it is apparent from the foregoing unsuccessfulprior art attempts to increase plant capacity and product quality, thata new technique is required to overcome the failures and difficultiesencountered, and simultaneously to provide for close product qualitycontrol and with an increase in plant capacity by eliminating thelengthy waiting time for laboratory evaluation of the various samples.

SUMMARY OF THE INVENTION The present invention overcomes both these andother prior art deficiencies by providing a novel and an improved systemfor continuously monitoring certain predetermined characteristics of aproduct and comparing thesecharacteristics with those simulated by areference standard by employing an electronic measuring system. Beforegoing into the various details of the specific system contemplated bythe present invention, it may be well to go into the theoreticalbackground of the present invention.

When a material is subjected to an alternating electrical field, itsresponse to the field can be described phenomenoiogically in terms of acapacitor and a resistor connected either in series or parallelrelation. The capacitor represents the materials ability to storeelectrical energy reversibly, while the resistor indicates theirreversible dissipation of electrical energy.

In a system of polar molecules, an alternating electrical field willcause displacements of the molecules from croscopic viscosity existingin the vicinity of the dipoles. It has been recognized that theelectrical resistivity of its inverse, the electrical conductivity, of asuspension of polar molecules in a nonpolar environment is directlyrelated to viscosity of the system. It is therefore possible tocorrelate changes in the electrical resistivity or conductivity of asystem to its internal or microscopic viscosity, provided the frequencyof the alternating field is less or smaller than the natural vibrationalfrequency of the polar molecules.

In the case of an asphalt air blowing process, it is important to notethat once on temperature and at a preselected frequency of lKHZ theresistance of the asphalt increases as air blowing progresses, while thecapacitance and hence, the dielectric constant of the asphalt remainsessentially constant. This confirms that the increased viscosity of theair blown asphalt is not due to oxidation of its constituents, but isdue to polymerization. For the purposes of this invention and forreasons obvious to those skilled in the art, frequencies ranging from 10to 10 HZ can be used, although frequencies of 10 to 10 HZ are preferredand frequencies between 500 and 50,000 HZ are most preferred.

Thus, it is seen that a material can be phenomeno- Iogically describedas a combination of a capacitor and a resistance, provided, of course,that the appropriate capacitance and resistance values are known at apreselected frequency, for example IKHZ. By ascribing characteristiccapacitance and resistance values to the two grades of asphalt (l80-oxand 220-ox), under consideration in regard to the preferred embodiment,it is possible to compare the electrical characteristics of an actualsystem undergoing air blowing with the predetermined desired finalelectrical equivalent. In this manner the extent of difference betweenthe two values indicates how far off the actual materials properties arefrom those of the desired finished product. To carry out the foregoingcomparison on a continuous basis, the present invention contemplatesemploying a monitoring system using a bridge circuit capable ofdetermining independently the unbalance of both the capacitive and theresistive component. Although the resistance comparison is the primeconsideration in this case, the capacitance reading is useful in thoseinstances involving chemical changes occurring during processing.

More specifically, the present invention contemplates continuouslymonitoring the electrical properties of the material by means of aconductivity sensing test cell. The sensed electrical properties of theactual material are compared electrically with a reference standardcomprising a combination resistor-capacitor network. Also, the referencestandard may comprise a sample of the finished product provided that theproduct material is stable under the prevailing physical conditions andits electrical properties remain constant with time. The test cell andthe reference standard are connected in an impedance bridgeconfiguration. A master oscillator and phasing system provide excitationof the bridge at the desired frequency. Bridge unbalance is sensed by apreamplifier whose output is fed to a demodulation or phase detectingsection. There the output signal is compared with the originalexcitation signal, and is resolved into a resistive and a reactivecomponent. This comparison is performed by means of phase sensitivedetectors whose outputs are used to drive the final displays or readoutdevices. The bridge excitation is accomplished by feeding the oscillatorsignal to an inverting amplifier and a noninverting amplifier, whichprovide out-of-phase and in-phase bridge excitation respectively. Sincenormally the test cell is located remotely from the reference standard,interconnecting coaxial cables are used wherever necessary. Theforegoing described system of the present invention has distinctadvantages over the prior art in that it is low in cost by virtue of thefact that it uses commercially available items, for example, the testcell; it is adaptable for use in multiple tank or tower operations; itis simple in that operator adjustments are minimal; it is weatherproofand provides a readily ascertainable null meter readout; it isserviceable since it is of a modular construction and employs solidstate devices and integrated circuits where possible; and it is safe inthat low voltages are used and is readily adaptable to explosion-proofconstructions. A further significant advantage of the present system isthat the control signals produced thereby are available for purposes ofautomation, if desired.

Accordingly, it is a primary object of the present invention to providea novel and improved system and method for determining by means of ameasuring technique when the desired end point of a particular materialor reaction has been obtained.

Another object of this invention is to provide a novel and improvedsystem and method for continuously monitoring by electronic means thedifference between selected characteristics of an actual material andpredetermined desired characteristics thereof, thereby to provide anindication as to when the material has attained the desired finalcharacteristics.

A further object of this invention is to provide a novel and improvedelectronic measuring system for monitoring continuously andautomatically the progress of a process employed in the manufacture of aproduct.

Still yet a further object of the present invention is to provide anovel and improved technique for electronically determining the endpoint of a material and which employs an electronic comparing circuitand an electric reference standard which simulates the desired end pointelectrical properties of the product to be produced at a givenfrequency.

. Having in mind the above and other objects that will be evident froman understanding of this disclosure, the invention comprises thedevices, combinations and arrangements of parts as illustrated in thepresently preferred embodiment of the invention which is set forth insuch detail as to enable those skilled in the art readily to understandthe function, operation, construction, and advantages of it when read inconjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof the present invention, in its broadest sense, connected in a bridgecircuit configuration;

FIG. 2 is a schematic block diagram showing a preferred embodiment ofthis invention; and

FIG. 3 is a schematic wiring diagram of the schematic of FIG. 2 showingthe details of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT In FIG. 1 there is disclosed aconventional bridge circuit configuration, generally denoted 10, of thehalfbridge type whose operation now will be described having referenceto the present invention. The bridge 11) comprises an input excitationtransformer T1 having a primary winding T1,, and a pair of split phasesecondary windings T1,, and T2, having a common grounded terminal 11.Each of the secondary windings T1, and T1,, are connected in one-half ofthe bridge circuit in series with impedances 12 and 13, and impedances14 and 15, respectively, and a common line 16 connecting a readoutdisplay such as a null meter M between common ground 11 and commonterminal 17. An excitation voltage signal E is applied to the primarywinding T1 and appears across the secondary windings as equal andopposite voltages, that is across the upper secondary winding T1, thereappears a voltage signal E having a phase angle of and across the lowersecondary winding T1 there appears a voltage signal E having a phaseangle of -l80. This input voltage is controlled and therefore can beconsidered as stable. Thus, there is formed a pair of commonly connectedsymmetrical circuits. The signal 13.492 generates a current i whichrepresents certain characteristics of the actual material being sampledby the test cell. The signal generates a current i, which representspredetermined simulated characteristics of the desired end product.These signals flow from each circuit through the common line 16 wherethey add vectorially and depending upon the phase angle relationshipbetween the respective signals, the meter M will provide a readoutrepresentative of this summation. The readout will permit determinationas to whether the desired end point has been obtained. A zero or nullreading will occur when the absolute values are identical and the phaseangles thereof are such that the vector summation is zero. If the phaseangle of the signal representative of the sampled material, which angleis determined by the ratio of resistive to reactive component, differsfrom that of the reference standard, then a readout other than zero willappear and the operator is aware that further processing is required.

FIG. 2 illustrates a block diagram of the system according to thepresent invention while FIG. 3 illustrates specific details thereof. Theelectrical properties of the sample material under test are monitored bya device such as a conductivity cell generally indicated as 20. The cellequivalent is shown in FlG. 3 by parallel'capacitor Ill-resistor22network. Preferably the test cell .comprises a plurality ofcapacitor-resistor (21-22;

21'-22', etc.) networks each of which has a different valuecorresponding to the desired grade of asphalt. A switch 27 may beprovided to permit the operator to select the appropriatecapacitor-resistor combination corresponding to'the desired grade to besampled. For example, to monitor separately the production of two grades(l80-ox and 220-ox) of oxidized asphalt, the desired softening pointspecifications for these two products and their corresponding typicalelectrical specifications at lKHZ are as follows:

a Softening Resistance Product Point Range, Capacitance Grade Range "FMcgohms PF ISO-ox l90-200 l.55-l.70 50:]

(R25) (C26) 220-ox. 220-230 2.70-2.80 50:1 (RZS) (C26') To accuratelydefine the desired physical characteristics of the finished product, itis important that a reliable laboratory test, such asAS TM' MethodD36-66T be employed in measuring the desired softening point for thispurpose. The reference standard 24, which simulates electrically thedesired physical characteristics of the finished product, comprises acombination of a parallel connected resistor 25 and a capacitor 26. Thestandard 24 in turn is connected in parallel with the test cell 241 toform in effect an impedance bridge configuration. As shown in FIG. 3 thestandard 24 may comprise a plurality of resistor-capacitor networks(25-26; 25-26, etc.) each of which corresponds to a different grade ofasphalt. A switch 23 is provided for selection by the operator of theparticular tower being tested.

A master oscillator 22 and a phasing section 29 provide excitation forthe bridge. Any bridge unbalance is sensed by a preamplifier 2s and istransmitted to a demodulation section generally indicates as 30 comprising a pair of phase sensitive detectors 31 and 32 whose operation iswell known and does not per se form part of this invention. The sensedsignal output of the preamplifier 26, which contains resistive andreactive components, is compared with corresponding components of theoriginal excitation signal supplied to the phase sensitive detectors 31and 32 from the phasing section 29 which receives the oscillator outputsignal. The comparison is performed by the phase sensitive detectors 31and 32 whose outputs, as indicated in FIGS. 2 and 3 are used to drivethe final displays or, in other words, to provide a meter readout 33 forthe capacitance and a meter readout 34 for the resistance. Thecapacitance is indicative of dielectric constant, while the resistance,which is the more significant readout, is indicative of viscosity. ifdesired, the capacitance readout 33 may be eliminated.

Physically, the electronic system is divided into two separate unitsreferred to as the measurement section and the readout section. Themeasurement section is located outdoors near the tanks or towers (notshown) housing the asphalt or other material undergoing manufacture.These units, as shown in FIG. 2, may be separated by quite some distanceD, for example, 200 feet.

The excitation circuit 35 comprises the amplifiers 36 and 37 which areof conventional solid state design. The incoming signal supplied by themaster oscillator 2b is fed to the inverting amplifier 36 andthenoninverting amplifier 37. These two amplifier circuits provideout-of-phase ((1,) and in-phase (1,) bridge excitation, respectively.Each amplifier may comprise a plurality of stages; however, the outputstage of each of these amplifiers preferably is connected in voltagefollower or common collector configuration to provide a low impedancedrive for the bridge. Also, the configuration of each channel isbalanced to provide a minimum of undesired signal quadrature, that is,unwanted components. These signals Q and l, are coupled to the referencestandard 24 and the test cell 20 by means of coaxial cables 38 and 39,respectively. This arrangement allows the sampling test cell and thereference standard to be located remotely from the excitation section35. Although the coaxial cables 38 and 39 may be of any reasonablelength, it is important that cable balance be maintained in the bridgelegs and thus, equal lengths of the same type of cable are essential inconnecting the cell 211 and the reference standard 24 to the excitationsection.

The preamplifier 26 functions as a bridge detector and may compriseamplifiers 4t) and 41, which preferably are arranged in a currentsensing operational configuration. This configuration is designed tofunction so that it provides stable current amplification. Any bridgeunbalance current flows into the input terminal 42 where it sees theoperationally developed virtual ground. The output voltage of thepreamplifier 26 then will comprise the product of the sensed bridgeunbalance current times the value of the feedback resistor 43. Theamplifier is an electrometer that is, it has a high input impedanceinput device connected in an inverting mode while the amplifier 41 is anoninverting fixed gain device that is used to increase the overall loopgain at the operating frequency. This arrangement provides for anextremely stable sensitive bridge detector. As shown in FIG. 3 thereference standard 24 and the test cell 20 are connected by means ofcoaxial cables 44 and and 46 to the input terminal 42 of thepreamplifier 26. As mentioned heretofore in regard to the input coaxialcables 38 and 39, the output coaxial cables 44 and 45 should be of equallengths and of the same type of cable in order to provide a properlybalanced system.

The readout section comprises the oscillator 28 which has excellentfrequency stability and purity of wave form and operates at about lKHZ.The oscillator per se is conventional. To provide greater sensitivityselection the oscillator output may be selectively fed to a suitableattenuator network provided with a switch to select either high or lowsensitivity. Although not shown, a voltage follower (common collectortransistor configuration) may be provided at the output of theoscillator 28 for purposes of line driving and impedance isolation. Suchconfigurations are characterized by high input impedance and low outputimpedance, thereby to provide the desired isolation.

The oscillator signal also is fed to a transformer 46 in the phasingsection 29 for use as the chassis reference signal. The primary ofthe'transformer 46 comprises a pair of series connected windings 47 and48 connected to ground 49. The secondary of the transformer 46 comprisesa single grounded winding 50 and a pair of windings 51 and 52 groundedat their common junction 53. The transformer 46 is constructed so thatthe single winding 50 provides a direct singal without any phase shift.The secondary windings 51 and 52 are connected in series relation withphase shifting network comprising a variable resistor 54 and a capacitor55, which by proper adjustment of the resistor 54, provides a 90 phaseshift of the reference signal applied thereto. The latter signal isshown as O in FIG. 3, while the nonphase shifted signal is shown by Apair of power amplifiers 56 and 57 are connected in the lines containingthe signals and Q respectively, to provide the necessary amplificationrequired to drive the reference input phase detector transformers 58 and59. Each transformer preferably comprises a pair of center tappedprimary windings and a pair of center tapped secondary windings. Thedetected bridge unbalance signal obtained from the preamplifier outputterminal 60 is processed by an amplifier 61. This amplifier 61 providesa relatively small gain, but more important, it compensates for fixedphase shifts that .may occur in the system. the amplifier 61 maycomprise one or more stages, and also may include a power amplifierstage if deemed necessary, to provide an input drive signal to thesignal input transformer 62 of the phase sensitive detectors 31 and 32.The primary of transformer 62 comprises a pair of windings 63 and 64grounded at their common junction 65. The secondary comprises pairs ofcenter tapped windings 66-67 and 68-69. The phase detectors operate insubstantially conventional fashion by comparing the input signal phasewith the corresponding phase of a reference excitation. The capacitancereadout meter 33 is connected between the center tapped secondaries oftransformers 58 and 62 (66-67) and the resistive readout meter 34 isconnected between the center tapped secondaries of transformers 59 and62 (68-69). Each meter 33,34 has a variable resistor 70,71,respectively, connected in series relation therewith for providing asensitivity adjustment. The outputs of the phase detectors 31 and 32 arebipolar DC signals which drive the readout devices which comprise DCmicroammeters 33 and 34, respectively. Since bridge balance isrepresented by zero output on each channel, zero center or a nullreading are normally used for purposes of readout. Thus, the operatorreadily can determine whether the actual product meets the desiredcharacteristics of the final product.

The foregoing described electronic measuring system achieves its purposeof eliminating the waiting period for analytical results, and, at thesame time, it insures much better product quality because the operatordoes not have to depend on arbitrary time limits for the variousoperating times required to produce the finished product. Thus, bymonitoring the readout meters 33 and 34 (although 34 alone issufficient), the operator readily can determine when the product isfinished and ready for transfer from the tower to the storage area orthe consumer.

While the present system has been described with specific reference toasphalt oxidization, it is within the scope of this invention to extendits usage to other areas such as the control of water content ofalcohols, esters and ethers; the control of the quality of solvents suchas isoparaffins; the control of oil content in waxes; and zinc dialkyldithiophosphate manufacture having an end point in neutralization of thecorresponding acid with zinc oxide, etc.

Further, it is within the scope of this invention to employ solid statedevices, such as transistors, diodes, etc., wherever possible and also,to use integrated circuits where available with the desiredcharacteristics. Although not specifically disclosed, it is within thescope of those skilled in the art to provide suitable conventional powersupply where necessary.

It will be understood that various changes in the details, materials,arrangements of parts, and operating conditions which have been hereindescribed and illustrated in order to explain the nature of thisinvention may be made by those skilled in the art within the principalscope of the invention as expressed in the claims.

Having thus set forth the nature of the invention, what we claim hereinis as follows:

1. An improved process for the oxidation of asphalt comprising the stepsof (l) maintaining the asphalt in a molten condition at an elevatedtemperature, (2) blowing air through said molten asphalt, (3) measuringthe electrical resistance characteristic of the asphalt as it is beingoxidized, (4) comparing the measured electrical resistancecharacteristic of the asphalt with a predetermined standard, and (S)terminating said blowing of air when said measured electrical resistancecharacteristic substantially corresponds to said predetermined standard.

2. The process according to claim 1, wherein the measured electricalresistance characteristic of the asphalt corresponds to viscosity of theasphalt.

2. The process according to claim 1, wherein the measured electricalresistance characteristic of the asphalt corresponds to viscosity of theasphalt.